Chair with recline control mechanism, recline limit control and back tilt mechanism

ABSTRACT

A chair having a recline control mechanism, a limit control apparatus and a tilt mechanism. The recline control mechanism operates to adjust resistance to rotation of a back assembly of the chair and includes an actuator lever having a lock structure attached to a movable spring assembly. Moving the spring assembly toward and away from a rotation axis for the back assembly adjusts the resistance. The limit control apparatus selectively limits the extent of rotation of the back assembly from about zero degrees to about 3.5 degrees to about seven degrees by using abutment surfaces. The tilt mechanism provides an independent and stable yet passive tilt capability to a backrest of the back assembly by using a pair of brackets, two pairs of links and two pairs of rods.

BACKGROUND OF THE INVENTION CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

1. Field of the Invention

The present invention relates to a chair with a reclining back assemblyand, more particularly, to a chair that includes a more efficientmechanism for adjusting resistance to the recline of a chair backassembly, a simple apparatus for limiting the angle of recline and atilt mechanism that results in a more comfortable passive tiltadjustment of a chair back in various chair recline positions.

2. Description of the Related Art

Reclinable office chairs are ubiquitous and appear in many differentstyles and designs and with many different functions. Most, if not all,include some mechanism to resist a reclining back. See for example, U.S.Pat. No. 6,053,574 which includes movable springs. Some chairs alsoinclude adjustable stops to control the angle of recline. See forexample, U.S. Pat. Nos. 6,616,231 and 6,193,314. Still other chairsinclude tiltable backs. See for example, U.S. Pat. Nos. 1,756,825 and3,938,858 and Reissue 36,335. Adjustable office chairs are sometimescomplicated to operate or are overly complex in structure and are oftenexpensive, unreliable or difficult to use.

BRIEF SUMMARY OF THE INVENTION

The difficulties encountered with previous devices have been over comeby the present invention. What is described here is a chair with areclining back including a seat assembly, a back assembly, a pivotforming structure defining an axis of rotation for allowing the backassembly to rotate relative to the seat assembly and a biasing structurefor resisting the rotation of the back assembly, the biasing structurebeing spaced from the axis of rotation and also being movable forwardlyand rearwardly relative to the axis of rotation with specific structuralelements as a way of controlling resistance to the rotation of the backassembly. The invention here also includes a limit control apparatushaving specific structure including a first structure having a stepconfiguration, a second structure including an abutment surface forengaging the first structure and an actuator for moving either the firstor second structures. The present invention further includes a tiltmechanism for the back of the back assembly including a first bracket, asecond bracket, a first pair of links, a second pair of links, a firstrod and a second rod so as to allow the second bracket which isconnected to the chair back to pivot in a plane generallyperpendicularly to the axes of the rods so as to provide a stable butpassive adjustment of the chair back as the back assembly reclines.

A complete understanding of the present invention and other objects,advantages and features thereof will be gained from a consideration ofthe present specification which provides a written description of theinvention, and of the manner and process of making and using theinvention, set forth in such full, clear, concise, and exact terms as toenable any person skilled in the art to which it pertains, or with whichit is most nearly connected, to make and use the same in compliance withTitle 35 U.S.C. section 112 (first paragraph). Furthermore, thefollowing description of a preferred embodiment of the invention read inconjunction with the accompanying drawing provided herein represent anexample of the invention in compliance with Title 35 U.S.C. section 112(first paragraph), but the invention itself is defined in the Claimssection attached hereto.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a rear isometric view of the inventive office chair describedherein.

FIG. 2 is a sectional elevation view of the chair shown in FIG. 1 in anupright position.

FIG. 3 is a sectional elevation view similar to that shown in FIG. 2 butwith the chair in a fully reclined position.

FIG. 4 is a front isometric view of controls and frame members of thechair shown in FIG. 1.

FIG. 5 is an enlarged top plan view of a box for the controls of thechair shown in FIG. 1.

FIG. 6 is an isometric view of the box shown in FIG. 5 and including abracket for attachment of the box to a support column.

FIG. 7 is an isometric view of an upper mount of the chair shown in FIG.1.

FIG. 8 is an exploded isometric of the elements shown in FIG. 4 but withthe absence of some elements.

FIG. 9 is an isometric view of a plastic slide plate.

FIG. 10 is an isometric view of the controls of the chair of FIG. 1showing a spring assembly absent a helical spring and a top cap.

FIG. 11 is an isometric view of an actuator lever for verticaladjustment of the chair shown in FIG. 1.

FIG. 12 is an isometric view of the top cap for the spring assembly ofthe chair shown in FIG. 1.

FIG. 13 is an isometric view of the helical spring used in the springassembly.

FIG. 14 is a downward looking isometric view of a spring guide for thespring assembly.

FIG. 15 is an upward looking isometric view of the spring guide shown inFIG. 14.

FIG. 16 is an isometric view of a spring carrier of the spring assembly.

FIG. 17 is an isometric view of a recline control mechanism for movingthe spring assembly.

FIG. 18 is an isometric view of an actuator lever of the recline controlmechanism.

FIG. 19 is a downward looking isometric view of a crank of the reclinecontrol mechanism.

FIG. 20 is a bottom view of the crank shown in FIG. 19.

FIG. 21 is a partial sectional view illustrating a lock structure in alocked position.

FIG. 22 is a view similar to FIG. 21 illustrating the lock structurebeing unlocked.

FIG. 23 is a view similar to FIGS. 21 and 22 illustrating the lockstructure in an unlocked position.

FIG. 24 is a view similar to FIGS. 21-23 illustrating the lock structurein an unlocked and moving position.

FIG. 25 is an isometric view of the recline control mechanism and thespring assembly in a position close to a recline rotation axis.

FIG. 26 is a view similar to FIG. 25 with the recline control mechanismand the spring assembly in a position further from the rotation axisthan is shown in FIG. 25.

FIG. 27 is a view similar to FIGS. 25 and 26 illustrating the reclinecontrol mechanism and the spring assembly in a position furthest fromthe rotation axis.

FIG. 28 is a rear isometric view of the controls shown in FIGS. 4 and 8and illustrating a limit control apparatus.

FIG. 29 is an isometric view of a brace of the limit control apparatus.

FIG. 30 is an isometric view of an actuator lever of the limit controlapparatus.

FIG. 31 is an isometric view of an abutment structure of the limitcontrol apparatus.

FIG. 32 is an isometric view of a slide block of the limit controlapparatus.

FIG. 33 is a diagrammatic elevation view of the actuator lever, theabutment structure, and the slide block of the limit control apparatus.

FIG. 34 is an exploded isometric view of a tilt mechanism for the chairshown in FIG. 1.

FIG. 35 is an isometric view of the tilt mechanism in an assembledcondition.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

While the present invention is open to various modifications andalternative constructions, the preferred embodiment illustrating thebest mode contemplated by the inventors of carrying out their inventionis shown in the various figures of the drawing and will be describedherein in detail, pursuant to Title 35 U.S.C. section 112 (firstparagraph). It is understood, however, that there is no intention tolimit the invention to the particular embodiment, form or example whichis disclosed herein. To the contrary, the intention is to cover allmodifications, equivalent structures and methods, and alternativeconstructions falling within the spirit and scope of the invention asexpressed in the appended Claims section attached hereto, pursuant toTitle 35 U.S.C. section 112 (second paragraph).

Referring now to FIGS. 1-3, there is illustrated a chair 10 having aback assembly 12, a seat assembly 14, a set of controls 16, a pair ofarms 18, 20, a support column 22, a base 24, and a set of casters 26,28, 30, 32, 34.

The illustrated chair 10 is of an office type which swivels, adjustsvertically, glides easily on a floor or carpet pad and includesreclining and tilt back features. The reclining and tilt back featuresare shown by comparing FIGS. 2 and 3 where in FIG. 2 the chair 10 isillustrated in a full upright position and in FIG. 3 the chair 10 isillustrated in a full recline position. The back assembly 12 goes froman angle of about 86 degrees from a reference vertical line 36 at fullupright to about 79 degrees at full recline, although other angles maybe used. The backrest 38 of the back assembly also reclines in amovement from about 10 degrees to about 24 degrees. It is noted that thebackrest 38 is independently able to tilt a maximum of about 7.2 degreeswhile undergoing a recline with the back assembly, although other anglesmay be employed. It is further noted that the reclining and the tiltback features may also be used on non-office chairs, for example, chairsused in conference centers, theaters or lecture halls where there may beno horizontal movement because the chairs are fixed to a floor or aplatform. The reclining and tilt back features may also be usedindependently of each other. For example, a chair may have the recliningfeature but not the tilt back and vice versa.

The backrest 38 may include a support panel 42 and a back cushion 44,the frame 40 may include a pair of parallel tubular frame members 46,48, and the back assembly 12 may include a tilt mechanism 50 connectingthe support panel 42 and the frame members 46, 48. The seat assembly 14may include a seat pan 52 and a seat cushion 54. It is noted that theback assembly may include only a panel of flexible and/or resilientmaterial such that a cushion is not needed. The same may be true of theseat assembly where only a seat panel of flexible and/or resilientmaterial is used.

The base 24 may include five arms 60, 62, 64, 66, 68 and a hub 70, andthe base rigidly supports the column 22 in the hub 70. The supportcolumn may include a gas cylinder for allowing vertical adjustment ofthe seat and back assemblies.

The set of controls 16 are located in and about a lower mount box 74,FIGS. 4, 5 and 6. The box 74 may include a pair of side walls 76, 78having lever openings 80, 82, 84, a front wall 86, a rear wall 88 and abottom wall 90. The box may also include a pair of horizontallyextending flanges 92, 94 with fastener receiving openings 96, 98, 100,102 for fasteners (not shown) to connect the box 74 to the seat pan 52.The bottom wall 90 may include a series of lock holes 103 extending overan arc of about 30 degrees measured from a fastener receiving hole 104located near the lever opening 80. Another fastener receiving hole 106may be placed near the lever opening 84. A longitudinally directed slot108 is formed in the center portion of the bottom wall 90 and a columnreceiving opening 110 is formed toward the rear of the bottom wall.Rigidly affixed to the bottom wall is a bracket 112 to which the supportcolumn 22 may be connected. The side walls 76, 78 also include twohorizontally aligned pivot openings 120, 122.

Pivotally mounted to the box 74 may be a U-shaped upper mount plate 126,FIGS. 4 and 7. The upper mount plate 126 includes a top wall 128, twoside walls 130, 132 and a rear wall 133, FIG. 8. The top wall includes alongitudinally directed slot 134 and the side walls include twohorizontally aligned pivot openings 136, 138. As shown in FIGS. 4 and 8,the pair of frame members 46, 48 are attached to the plate 126 by anysuitable technique such as by welding. A pivot rod 140 may be insertedinto the aligned openings 120, 122 of the box 74 and the alignedopenings 136, 138 of the plate 126. This arrangement, a pivot formingstructure, allows the back assembly 12 to recline relative to theremainder of the chair, and in particular, relative to the seat assembly14, the support column 22 and the base 24 as is typical of an officechair.

The pivot forming structure of the control box 74, the plate 126 and thepivot rod 140 creates an axis of rotation 142, FIGS. 2 and 3, that iscoincident with the longitudinal axis of the pivot rod 140. This pivotaxis is located forward of the support column 22. As seen in FIGS. 2 and3, the axis of rotation 142 is under the forward portion of the seatassembly 14. In one embodiment the rotation axis 142 is about 6.125inches forward of a vertically aligned longitudinal axis 144, FIGS. 2and 3 of the column 22.

Located within the box 74 may be a low friction plastic slide plate 150,FIGS. 8 and 9, a slidable spring assembly 152, FIGS. 2, 3, 8 and 10, arecline control mechanism 154, FIGS. 8 and 10, for moving the springassembly forward toward the rotation axis 142 and rearward away from therotation axis. The slide plate 150 includes a longitudinal slot 160extending forwardly and rearwardly which is parallel to and aligned withthe slot 108 of the box 74 and the slot 134 of the plate 126. The slideplate 150 may also include an opening 165 to receive the bracket 112, afirst fastener pass-through hole 164 that aligns with the hole 104 ofthe box 74, a second fastener pass-through hole 166 that aligns with thehole 106 of the box 74, a series of detent recesses 168, two upstandingflanges 170, 172, a lateral slot 174 along the rear portion of the slideplate and a cut-out 176 to expose the lock holes 103. It should be notedthat the lock holes may be formed in the slide plate and thus thecut-out may be obviated.

Extending from lever opening 82, FIG. 5, of the box 74 may be anactuator lever 180, FIGS. 4, 8 and 10, for adjusting the vertical heightof the seat and back assemblies. Extending from the lever opening 80 isan actuator lever 182, part of the recline control mechanism 154 forcontrolling resistance to rotational movement of the back assemblyduring recline, and extending from the lever opening 84 is an actuatorlever 184 for limiting the degree of rotation of the back assembly.

The actuator lever 180 may include a handle portion 190, FIG. 11, afulcrum portion 192 and a bearing portion 194. The fulcrum portionincludes a hole 196 for receiving a pin 197, FIG. 18, that pivotallymounts the actuator lever 180 to the flanges 170, 172 of the slide plate150. The bearing portion 194 operates the air cylinder in the usualfashion known by those skilled in the art.

The spring assembly 152 is a biasing structure and may include a springcarrier 200, FIGS. 8, 10 and 16, having a tab portion 202 with a pinreceiving opening 204 and a slot 205, a spring guide 206, FIGS. 8, 10,14 and 15 with a post portion 208, a cup portion 210 and a runnerportion 212, a top cap 214, FIGS. 8 and 12, with a central opening 216,and a helical spring 218, FIG. 13. The helical spring 218 is mountedaround the post portion 208 and is supported by the cup 210. The postportion 208 extends through the central opening 216 of the top cap 214.The runner portion 212 of the spring guide 206 extends through the slot205 of the spring carrier 200. The runner portion 212 extends into thelongitudinal slot 160 of the slide plate 150 and is guided and limitedby the slot 160. The upper end of the post portion 208 extends out ofthe central opening 216 of the top cap 214 and into the slot 134 of theplate 126. The spring may be made of flattened steel wire, 3 inches inlength with a spring constant of 375 pounds per inch of deflection. Itis to be noted that other types of energy devices may be used instead ofthe helical spring, such as a rubber spring or an air spring.

The recline control mechanism 154 has a “lost motion” feature and mayinclude the actuator of lever 182 having a handle portion 220, FIGS.17-20 attached to a link portion 222. Also included is a crank 224mounted above the actuator lever 182. The link portion 222 has a crankpin 226, a spring pin 228, two lock ball openings 230, 232, a bridgewall 234 between the lock ball openings, a tab cutout 236 and a fasteneropening 238.

The crank 224 may include a fastener receiving opening 240, FIGS. 19 and20 to allow the crank to pivot independently of the handle portion 220and the link portion 222. The crank also includes a tab recess 242 witha fastener receiving opening 244, a crank pin slot 246, a U-shapedgroove 248 and a ball cage flange 250 with a ball receiving slot 252.The recline control mechanism 154 also includes a lock ball 254 and awire spring 256, FIGS. 8, 10 and 17. The lock ball 254, the ball cageflange 250, the bridge wall 234 and the openings 230, 232 form a lockstructure. The wire spring 256 fits into the groove 248 and includes twolegs 257, 258, FIG. 8, that are pre-loaded to engage the spring pin 228so that movement of the spring pin 228 flexes one or the other of thelegs 257, 258 to create a return biasing force acting on the crank 224and thereby the lock ball 254. A shoulder bolt 259, FIG. 10, extendsthrough the openings 238, 240 in the link portion 222 and the crank 224pivotally connecting these elements to the box 74 by threading into thehole 104. Another bolt 260, FIG. 10, extends through the opening 204 inthe carrier 206 and the opening 244 in the tab recess 242 of the crank224 to pivotally connect the carrier 200 and the crank 224.

In operation, the actuator lever 182 is able to rotate a short distance,about 3-4 degrees about the bolt 259 in a first step so as to remove anyrestraint on the lock ball 254 exerted by the bridge wall 234. As shownin sequence in FIGS. 21-24, the bridge wall 234 depresses the lock ball254 in one of the lock holes 103 of the box 74 to lock the reclinecontrol mechanism 154 and the spring assembly 152. As the actuator lever182 is rotated, the bridge wall 234 moves away from the lock ball 254 sothat the lock ball is located under either the opening 230 or theopening 232. After the bridge wall 234 rotates out of the way, the lockball 254 is able to be moved from one of the lock holes 103 in thebottom wall 90 of the box 74 to another lock hole. As rotation of theactuator lever continues, the crank pin 226 of the link portion 222engages one or the other ends 261, 262 of the wall surrounding the crankslot 246. The crank 224 then moves causing the spring assembly 152 tomove along the slot 160 of the slide plate 150. Motion is transmitted tothe spring assembly 152 through the carrier 200 which is connected tothe crank 224 by the shoulder bolt 260. The wire spring 256 ensures thatafter movement of the spring assembly, the actuator lever 182 will bebiased back to a locking position where the bridge wall 234 again bearsdownwardly on the lock ball 254 so as to drop it into one of the lockholes 103 in the bottom wall 90 of the box 74.

The purpose of the spring assembly 152 is to resist rotation of the backassembly 12 about the rotation axis 142. The further the spring assemblyis from the rotation axis, the greater is the moment arm and the higheris the resistance to the reclining back assembly. By moving the springassembly closer to the rotation axis, the moment arm is decreased andrecline of the back assembly is more easily accomplished. Thisarrangement for altering the tension applied to the back assembly issimple, robust, reliable and very easy to use. The control may beaccessed from the side of the chair instead of from under the chair andoperation merely requires a lever to be pivoted with an attendantmechanical advantage instead of a knob to be rotated. This feature alsoprovides a user easy feedback to easily judge the current tension orresisting force and then to alter the force, if desired. Also, movingthe lever forward to decrease tension and rearward to increase tensionmay be displayed graphically on the handle portion 220 which is easilyseen by a chair user. This compares favorably to an under chair knobwithout any indication of the correct direction of rotation and with thegreat difficulty in determining the comfort level of the recline once anadjustment is made.

The user determines his/her comfort level by moving the lever forward orrearward while attempting to recline. When the amount of resistanceforce is found to be suitable, the user releases the handle portion 220of the actuator lever 182. The wire spring 256 returns the actuatorlever to an at-rest position where the bridge wall 234 is positionedover the lock ball 254 causing the lock ball to be depressed into one ofthe six lock openings 103. This locks the crank 224, and the actuatorlever 182, and thereby the spring assembly 152, into position relativeto the rotation axis 142. The distance of the spring assembly from thepivot axis defines the amount of resistance that the spring assemblyoffers to oppose the rotation of the back assembly 12. Movement of theactuator lever 182 and the spring assembly 152 is shown in FIGS. 25, 26and 27. Total linear movement of the spring assembly may amount to about0.75 inches.

The lock structure may take any of a number of forms. For example, alock structure may be formed by a detent arrangement like that used withthe actuator lever 184 as explained below in relation to the detentrecesses 168 in the slide plate 150. Or, a lock structure may be formedof high friction material or friction increasing surface textures. Therotation or recline force applied by a chair user is somewhat obliquethereby creating a force component acting in the direction of therotation axis 142. The greater the recline angle, the greater will bethe force component. The lock structure must be sufficient to resist theforce component and any one of various mechanisms may provesatisfactory.

It is also noted that the amount of force needed to compress the spring218 is a function of the distance between it and the rotation axis 142.In addition, the further the distance from the rotation axis, thegreater must be the deflection or compression of the spring to reach adesired recline. This greater compression distance adds a component tothe total force resisting recline of the back assembly.

The chair 10 may also include a limit control apparatus 270, FIGS. 4, 8,10 and 28-33, for determining the extent of allowable recline or toprevent any recline at all. There may be three limits or stops which achair user may select for limiting the amount of rotation of the backassembly from zero degrees, no recline, for tasking, to about 3.5degrees for tasking or conferencing to about 7 degrees, full recline,for conferencing or lounging.

The limit control apparatus 270 may include an actuator structure orlever 184 with a handle portion 274 and a link portion 276, a slideblock 278, a brace 280 and a stepped abutment structure 282. The linkportion 276 has a first end portion 284 with a fastener receivingopening 286 connected to the handle portion 274, and a second endportion 288 with a slot 290. The fastener receiving opening accommodatesa shoulder bolt 292, FIG. 10, to connect the actuator structure 272 tothe box 74 through hole 106 and to establish a pivot axis 294. The linkportion 276 also includes a small foot 295 to engage the detent recesses168 in the slide plate 150 to ensure the proper location and retention.The slide block 278 has a base portion 296, a pin 298, an upstandingprojection 300 and a rail 302. The rail 302 rides in the lateral slot174 of the slide plate 150, FIGS. 8 and 10. The pin 298 is received bythe slot 290 of the link portion 276 for transforming rotational motionof the handle portion 274 to linear motion of the slide block 278. Thebrace 280 is affixed to the frame members 46, 48 of the back assembly 12and the stepped abutment structure 282 is connected to the brace 280.

The upstanding projection 300 of the slide block 278 may include anabutment surface 304, and the abutment structure 282 includes threecomplementing abutment surfaces 306, 308, 310, each abutment surface ofthe abutment structure being at a different elevation from the other twosurfaces. The abutment surfaces are generally horizontal when the chairis in an upright position, however, because of the recline of the backassembly, the shorter abutments topped by the surfaces 308, 310 areslanted at about 3.5 and 7 degrees, respectively so that contact is madealong generally the entire surfaces. It is noted that the abutmentstructure 282 may be mounted on the box and the slide block 278 may bemounted on the back assembly 12, if found desirable.

In operation, the limit control apparatus 270 functions by pivoting thehandle portion 274 through a maximum arc of about 21 degrees about thepivot axis 294. Rotation of the handle portion is translated to linearmotion of the slide block 278 and moving the slide block allowsselective placement of the upstanding projection 300 opposite one ofthree abutment surfaces 306, 308, 310 of the abutment structure 282.Because the abutment structure is affixed to the back assembly 12,rotation of the back assembly is selectively limited. When the abutmentsurface 306 of the abutment structure 282 is aligned with the abutmentsurface 304 of the upstanding projection 300, the back assembly will notbe able to recline. When the abutment surface 308 is aligned with theupstanding projection 300, the back assembly will be able to be reclinedabout 3.5 degrees. When the abutment surface 310 is aligned with theupstanding projection 300, the back assembly will be able to be reclinedfully, about 7 degrees. The limit control apparatus is very easy tooperate, is very reliable and is robust.

The tilt mechanism 50 is based on a four bar mechanism, and may includea first or frame bracket 322, a second or backrest bracket 324, a firstor upper pair of links 326, 328, a second or lower pair of links 330,332, a first or upper pair of structures, such as rods 334, 336, and asecond or lower pair of structures, such as rods 338, 340. The tiltframe bracket 322 is secured to the frame members 44, 46 in anyconvenient fashion. The backrest bracket 324 is connected to the supportpanel 42 and allows the back to pivot in a plane generally perpendicularto longitudinal axes 342, 344, 346, 348 of the rods in reaction to themovement of a chair user's back.

The frame bracket 322 includes a first or upper pair of holes 350, 352and a second or lower pair of holes 354, 356. The front upper rod 336 ispivotally connected to the frame bracket through the upper holes 350,352 such that the pivot axis 344 of the rod 336 does not translate. Thefront lower rod 340 which is pivotally connected to the frame bracketthrough the lower holes 354, 356, such that the pivot axis 348 of therod 340 is also restrained from translating. The frame bracket 322 mayalso include a first or upper pair of cutouts in the form of curvedslots 358, 360 and a second or lower pair of cutouts in the form ofslots 362, 364.

The back bracket 324 includes a first or upper pair of holes 366, 368, asecond or lower pair of holes 370, 372, a first or upper pair of cutouts374, 376 and a second or lower pair of cutouts 378, 380. Each link 326,328, 330, 332 includes a first or front end portion 390, 392, 394, 396and a second or rear end portion 398, 400, 402, 404.

The front end portions 390, 392 of the upper links 326, 328 may includerod openings 410, 412 which receive the front upper rod 336. The rearend portions 398, 400 of the upper links 326, 328 includes rod openings414, 416 which receive the rear upper rod 334. The front lower rod 340is received by openings 418, 420 in the front end portions 394, 396 ofthe lower links 330, 332 and the rear lower rod 338 is received byopenings 422, 424 in the rear end portions 402, 404 of the lower links330, 332.

The upper rear pivot axis 342 is allowed to travel within the arcgenerally defined by the pair of upper curved slots 358, 360 in theupper portion of the frame bracket 322. The lower rear pivot axis 346 isallowed to travel along an arc generally defined by the pair of curvedlower slots 362, 364 in the frame bracket 322. The upper front rod 336moves in the cutouts 374, 376 of the backrest bracket 324 and the lowerfront rod 340 moves in the cutouts 378, 380 of the backrest bracket 324.The upper links 326, 328 are able to pivot about the pivot axis 344 andthe lower links 330, 332 are able to pivot about the pivot axis 348. Thepivot axes 344, 348 allow the upper pair of links 326, 328 to rotateabout 40 degrees downwardly until limited by the ends of the upper slots358, 360, and the lower pair of links 330, 332 also rotate about 40degrees downwardly. At rest, the ends of the lower slots 362, 364 limitrotation of the backrest bracket 324. These rotations combine to allowthe backrest bracket 324 to pivot about 7 to 8 degrees in a planegenerally perpendicular to the pivot axes 342, 344, 346, 348. Thiscreates a stable, wobble-free platform for the backrest 38.

The effect of the two-dimensional movement of the backrest bracket 324is that the chair back follows and supports the back of the chair userwith little shear so that there is little or no “shirt pull” of thegarment being worn by the chair user even when the user fully reclinesthe back assembly. This rotational adjustment feature of the back isvery stable, passive and functions with chair users of various sizes.

The above specification describes in detail a preferred embodiment ofthe present invention. Other examples, embodiments, modifications andvariations will, under both the literal claim language and the doctrineof equivalents, come within the scope of the invention defined by theappended claims. For example, different lever, link and mechanismdesigns are considered equivalent structures and will also come withinthe literal language of the claims. The same applies to the dimensionsand physical charcteristics mentioned as well as the amount of reclineand tilt. Still other alternatives will also be equivalent as will manynew technologies. There is no desire or intention here to limit in anyway the application of the doctrine of equivalents nor to limit orrestrict the scope of the invention.

1. A chair with a reclining back comprising: a seat assembly; a backassembly including a frame member connected to said seat assembly; apivot forming structure defining an axis of rotation for allowing saidback assembly to rotate relative to said seat assembly; and a biasingstructure for resisting the rotation of said back assembly, said biasingstructure being spaced from said axis of rotation of said back assemblyand being movable forwardly toward said axis of rotation and rearwardlyaway from said axis of rotation for controlling resistance to rotationof said back assembly.
 2. The chair of claim 1 including: an actuatorstructure connected to said biasing structure for moving said biasingstructure.
 3. The chair of claim 1 including: a lock structure connectedto said biasing structure for locking said biasing structure in aselected position.
 4. The chair of claim 1 including: a lock structureconnected to said biasing structure for locking said biasing structurein a selected position; and an actuator structure connected to saidbiasing structure and to said lock structure for selectively locking andunlocking said lock structure and for moving said biasing structure. 5.The chair of claim 1 wherein: said pivot forming structure includes alower mount and an upper mount.
 6. The chair of claim 1 wherein: saidbiasing structure includes a spring.
 7. The chair of claim 1 including:a lock structure connected to said biasing structure for locking saidbiasing structure in a selected position; and an actuator structureconnected to said biasing structure and to said lock structure forselectively locking and unlocking said lock structure and for movingsaid biasing structure; and wherein said pivot forming structureincludes a lower mount and an upper mount.
 8. The chair of claim 7wherein: said biasing structure includes a spring.
 9. The chair of claim1 including: a limit control apparatus connected to said back assemblyand to said pivot forming structure for limiting recline of said backassembly.
 10. The chair of claim 9 wherein: said limit control apparatusincludes a first structure having a stepped configuration with aplurality of abutment surfaces, each of said abutment surfaces beingdisposed in a generally horizontal attitude, said first structure beingconnected to either a chair lower mount or to the reclining backassembly; a second structure including an abutment surface forselectively engaging said abutment surfaces of said first structure,said abutment surface of said second structure being disposed in agenerally horizontal attitude; and an actuator structure being connectedeither to said first structure or to said second structure forcontrolling engagement of said first and said second structures.
 11. Thechair of claim 10 wherein: said actuator structure is rotatable about agenerally vertical axis; and said second structure slides linearly inresponse to movement of said actuator structure.
 12. The chair of claim11 wherein: said second structure includes a projection forming saidabutment surface, a slidable base for mounting said projection and apost connected to said base and to said actuator structure.
 13. Thechair of claim 12 wherein: said second structure is mounted to a chairlower mount and said first structure is mounted to said back assembly.14. The chair of claim 1 wherein: said back assembly includes a tiltmechanism for maintaining said back assembly in contact with a chairuser during recline of said back assembly.
 15. The chair of claim 14wherein: said tilt mechanism includes a first bracket affixed to a framemember that is part of said back assembly, said first bracket having afirst pair of holes and a second pair of holes; a second bracketpivotally mounted to said first bracket and affixed to a back of saidback assembly, said second bracket having a first pair of holes and asecond pair of holes; a first pair of links, each link of said firstpair of links having first and second end portions; a second pair oflinks, each link of said second pair of links having first and secondend portions; a first structure for pivotally connecting said firstbracket through said first pair of holes and said first end portions ofsaid first pair of links; a second structure for pivotally connectingsaid second bracket through said first pair of holes and said second endportions of said first pair of links; a third structure for pivotallyconnecting said first bracket through said second pair of holes and saidfirst end portions of said second pair of links; and a fourth structurefor pivotally connecting said second bracket through said second pair ofholes and said second end portions of said second pair of links.
 16. Thechair of claim 15 wherein: said first structure includes a first rod;said second structure includes a second rod; said third structureinclude a third rod; and said fourth structure includes a fourth rod.17. The chair of claim 16 wherein: said first rod is mounted in saidfirst pair of holes of said first bracket and in holes of said first endportions of said first pair of links; said second rod is mounted toholes in said second end portions of said first pair of links and insaid first pair of holes of said second bracket; said third rod ismounted in said second pair of holes of said first bracket and to holesin said first end portions of said second pair of links; and said fourthrod is mounted to holes in said second end portions of said second pairof links and in said second pair of holes of said second bracket. 18.The chair of claim 9 including: a tilt mechanism for maintaining saidback assembly in contact with a chair user during recline of said backassembly.
 19. The chair of claim 18 wherein: said tilt mechanismincludes a first bracket affixed to a frame member that is part of saidchair back assembly, said first bracket having a first pair of holes anda second pair of holes; a second bracket pivotally mounted to said firstbracket and affixed to a back of said back assembly, said second brackethaving a first pair of holes and a second pair of holes; a first pair oflinks, each link of said first pair of links having first and second endportions; a second pair of links, each link of said second pair of linkshaving first and second end portions; a first structure for pivotallyconnecting said first bracket through said first pair of holes and saidfirst end portions of said first pair of links; a second structure forpivotally connecting said second bracket through said first pair ofholes and said second end portions of said first pair of links; a thirdstructure for pivotally connecting said first bracket through saidsecond pair of holes and said first end portions of said second pair oflinks; and a fourth structure for pivotally connecting said secondbracket through said second pair of holes and said second end portionsof said second pair of links.
 20. The chair of claim 19 wherein: saidfirst structure includes a first rod; said second structure includes asecond rod; said third structure include a third rod; and said fourthstructure includes a fourth rod.
 21. A limit control apparatus for areclining back assembly of a chair comprising: a first structure havinga stepped configuration with a plurality of abutment surfaces, each ofsaid abutment surfaces being disposed in a generally horizontalattitude, said first structure being connected to either a chair lowermount or to the reclining back assembly; a second structure including anabutment surface for selectively engaging said abutment surfaces of saidfirst structure, said abutment surface of said second structure beingdisposed in a generally horizontal attitude; and an actuator structurebeing connected either to said first structure or to said secondstructure for controlling engagement of said first and said secondstructures.
 22. The apparatus of claim 21 wherein: said actuatorstructure is rotatable about a generally vertical axis; and said secondstructure slides linearly in response to movement of said actuatorstructure.
 23. The apparatus of claim 22 wherein: said actuatorstructure includes a handle and a link, said link having a first endportion pivotally connected to said handle and a second end portionhaving a slot for pivotal engagement with said second structure.
 24. Theapparatus of claim 23 wherein: said second structure is mounted to achair lower mount and said first structure is mounted to the backassembly.
 25. The apparatus of claim 21 wherein: said second structureincludes a projection forming said abutment surface, a slidable base formounting said projection and a post connected to said base and to saidactuator structure.
 26. The apparatus of claim 21 wherein: said actuatorstructure is rotatable about a generally vertical axis; said secondstructure slides linearly in response to movement of said actuatorstructure; and said second structure includes a projection forming saidabutment surface, a base for mounting said projection and a postconnected to said base and to said actuator structure.
 27. The apparatusof claim 26 wherein: said second structure is connected to a lower mountand said first structure is mounted to the back assembly.
 28. A tiltmechanism for a chair back comprising: a first bracket adapted to beaffixed to a chair frame member that supports the chair back, said firstbracket having a first pair of holes and a second pair of holes; asecond bracket pivotally movably mounted to said first bracket adaptedto be affixed to the chair back, said second bracket having a first pairof holes and a second pair of holes; a first pair of links, each link ofsaid first pair of links having first and second end portions; a secondpair of links, each link of said second pair of links having first andsecond end portions; a first structure for pivotally connecting saidfirst bracket through said first pair of holes and said first endportions of first pair of links; a second structure for pivotallyconnecting said second bracket through said first pair of holes and saidsecond end portions of said first pair of links; a third structure forpivotally connecting said first bracket through said second pair ofholes and said first end portion of said second pair of links; and afourth structure for pivotally connecting said second bracket throughsaid second pair of holes and said second end portions of said secondpair of links.
 29. The tilt mechanism of claim 28 wherein: said firststructure includes a first rod; said second structure includes a secondrod; said third structure includes a third rod; and said fourthstructure includes a fourth rod.
 30. The tilt mechanism of claim 29wherein: said second bracket is restricted to move in a two-dimensionalplane generally perpendicular to longitudinal axes of said first, saidsecond, said third and said fourth rods.